Pump system

ABSTRACT

A pumping system employs the method of using an inoffensive fluid as a displacing fluid to pump an offensive fluid to be displaced. The system is illustrated in a well pumping operation and includes a pump structure for establishing a moving fluid interface between the displacing fluid and the well fluid to be displaced from the well reservoir so that the displacing fluid functions as a piston to pump well fluid to well surface. A gas elimination system and a diluent injection system may be associated with the pump structure to remove gas evolved from the well fluid and to inject a diluent into the well fluid reservoir to reduce well fluid viscosity.

Apr. 9, 1974 United States Patent [1 1 Greer 1 PUMP SYSTEM PrimaryE.\'aminerW'il1iam L. Freeh Assistant E\'aminerLeonard Smith [22] Filed:

Attorney, Agent, or Firm-l-luebner & Worrel [57] ABSTRACT A pumpingsystem employs the method of using an in- 417/431 [51] Int. F09b 35/02417/92, 99, 101-103,

offensive fluid as a displacing fluid to pump an offen- [58] Field ofSearch................

sive fluid to be displaced. The system is illustrated in a well pumpingoperation and includes a pump structure for establishing a moving fluidinterface between the displacing fluid and the well fluid to bedisplaced from References Cited the well reservoir so that thedisplacing fluid functions as a piston to pump well fluid to wellsurface. A gas elimination system and a diluent injection system may beassociated with the pump structure to remove gas 417/313 X evolved fromthe well fluid and to inject a diluent into 4l7/92 the wellfluidreservoir to reduce well fluid viscosity. 417/92 S T m N m E m M m m Sdn .i .1 T ms ow A nfimwnmm T e weo SFDHTPB D E93 O64 T265226 999999NHHHHHH U 79947- 223349 85 33 787 9 996576 32 3 31 Claims 10 DrawingFigures PATENTEDAPR 9 1974 SHEET 5 BF 6 PUMP SYSTEM BACKGROUND OF THEINVENTION The present invention relates to pumps and pumping 5 methodsand more particularly to a pump and pumping method suitable for use indownhole well pumping operations, such as oil well pumping operations,as well as in other pumping operations.

Heretofore, various types of pumps have been devised for pumping wellfluids, such as crude oils. Unfortunately, the crude oil pumped isoftentimes of an extremely offensive nature containing variousimpurities such as sand, silt, sludge, and salt water so as to beabrasive and/or corrosive. A problem common with the design of many ofthese prior art pumps has been that they have included moving parts,such as plunger mechanisms, which contacted the offensive fluids beingpumped. Thus, as a consequence, the offensive crude oils or well fluidshave generally caused considerable wear, excessive friction, andcorrosion ofthe parts, particularly the moving parts, of the prior artpumps. Considerable expense, therefore, has generally been associatedwith the use of these prior art pumps in such well pumping operationswhere an offensive well fluid is being pumped since the pumps had to befrequently shut down, removed from their downhole locations, and rebuiltor repaired to change and replace their worn and/or corroded movingparts.

Additionally, many prior art pumps constructed for well pumpingoperations have been designed so that the displacing well fluid iscaused to 'move upward in physical contact with a reciprocating suckerrod string. Unfortunately, the contact of the well fluid which wasgenerally of a high viscosity with the sucker rod string acted torestrict the downward movement, so called rod fall, of the sucker rodstring, and thereby severely restricted the upper cycle rate at whichthe plunger could be driven in these pumps to pump well fluid to thewell surface. Further, substantial stress was placed on the sucker rodstring by the downward movement of a pumping jack to which it wasconnected since the upward flowing well fluid resisted the sucker rodstrings downward movement. Consequently, pump outputs 1 prior to thistime have been limited-since it has not been possible to exceed rod fallrates greater than approximately three strokes per minute withoutrunning the danger of breaking the sucker rod string.

Other problems common with prior art downhole well pumps have been thatthey have been subject to being locked up by gas locks caused by gasevolved from the pumped well fluid and by the paraffin occurring inparaffin based crude oils. Additionally, prior art pumps have beenunsuitable to pump extremely high viscosity crude oil mixtures, such assand laden crude oils, since in order to avoid excessive wear fromcontact with the high viscosity well fluids filtering mechanisms wereemployed to filter the impurities from the oil and these filtersunfortunately restricted to a significant extent oil flow into the pump.

SUMMARY OF THE INVENTION movable pump parts with the offensive fluid soas to substantially reduce friction, pump wear, and pump corrosion.

It is further an object of the present invention to provide an improvedpump suitable for downhole use which is operable to establish andmaintain an interface between a displacing fluid and a fluid to bedisplaced and to displace this interface in a reciprocal motion so thatthe displacing fluid functions at the interface as a piston to preventgas lock and pump the displaced fluid to a selected location.

It is, additionally, an object of the present invention to provide animproved pump for downhole use which utilizes a displacing fluid to pumpwell fluid to well surface and is arranged for connection with a suckerrod string isolated from the well fluid, thereby to obviate theaforementioned disadvantages inherent with the prior art pumps havingwell fluid pumped to well surface in contact with the sucker rod string.

It is still another object of the present invention to provide animproved method for removing crude oil from an oil well reservoir, suchas an oil well reservoir containing unconsolidated reservoir sands, inwhich the crude oil-impurity mixture in the well reservoir is pumped towell surface without separation or filtration.

It is also an object of the present invention to provide an improved gaselimination system for use with down hole pumps which operates to removegas evolved from the well fluid from the pump thereby to prevent gaslocks.

It is another object of the present invention to provide an improvedfluid injection system for use with a downhole pump which operates toinject controlled quantities of a diluent into a well fluid being pumpedso as to dilute anddecrease the viscosity of the well fluid.

It is yet another object of the present invention to provide an improvedmethod for pumping a fluid to be displaced which employs the concept ofusing a displacing fluid which may be miscible with the displaced fluidto pump the displaced fluid to a selected location.

In accomplishing these and other objects, there is pumping systemsuitable for pumping an offensive fluid. The term offensive fluidas'used herein refers to any fluid the contact of which with pump parts,particularly moving parts, is considered undesirable and detrimental tothe pump. Examples of such offensive fluids are abrasive and erosivehigh viscosity fluids, corrosive acids, etc. The fluid which is of anoffensive nature may be a high viscosity sand bearing crude oil. Thepumping system provided is for a well pumping operation and includes asucker rod string mounted in a fluid sealed tubing string so as to beisolated from well fluid. A pump structure is mounted on the lower endof the tubing housing of the sucker rod string. The pump structureincludes a first chamber housing a plunger which is connected by adownwardly extending passage to a lower second or discharge chamber. Thedischarge chamber has port means through which the crude oilimpuritymixture forming the well fluid in the well reservoir may be pumped intothe chamber-and then discharged to a'point isolated from the oilreservoir. The discharge point is connected in communication with wellsurface through a production tubing string. Means are included forsupplying a controlled amount of displacing fluid of an inoffensivelubricating nature, which preferably is kerosene, to the plunger chamberso that a fluid interface region is formed between the kerosene and thecrude oil in the downward extending passage.

tubing string. Since gas is oftentimes evolved from they well fluid, agas trap may be associated with the upper end of the downward extendingpassage and a valve operated conduit may be connected with the gas trapto selectively conduct trapped gas to a portion of the discharge chamberwhere it will be pumped with the crude oil up the production tubingstring. It has been found however, that the replenishment of thedisplacing fluid 4 FIG. 5 is a view taken along the line 5-5 of FIG.312;

FIG. 6 is a view taken along the line 6-6 of FIG. 3b;

FIG. 7 is a view taken along the and FIG. 8 is a side elevation view ofa portion of the pumping system of FIG. 1 which has been modified toinclude a diluent injection assembly and which is partially cut away toillustrate the internal construction of the diluent injection assembly.

line 77 of FIG. 3a;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to thedrawings in more detail, there is shown in FIGS. 1-7 a well pumpingsystem generally designated by the numeral 11 positioned in the bore orcasing 13 of an oil well. The pumping system 11 has vertically extendingtubing strings 15 and 17 positioned within the well bore 13 to extendfrom the surface of r the well to the bottom region of the well whereatwell to maintain the displacing fluid crude oil interface inherentlyoperates to prevent the pumping system from gas locking. Additionally, afluid injection system may be associated with the pump structure forinjecting a diluent fluid into the high viscosity crude oil so as todilute the crude oil and thereby reduce its viscosity. Thus, there isprovided pumping system and method of pumping wherein limited contact ismade between the offensive fluid displaced and the moving'parts of thepumping mechanism. Additionally, a pumping system is provided which issuitable for removing crude oil by the method-of pumping a crudeoil-impurity mixture without separation from a well reservoir to wellsurface, thereby to significantly enhance oil producing rates from wellreservoirs characterized by being high viscosity fluent mixtures ofcrude oil with impurities such as oil well reservoirs containingunconsolidated reservoir sands.

Additional objects of the present invention reside in the specificconstruction and method of operation of the exemplary well-pumpingsystem hereinafter particularly described in the specification and shownin the several drawings.

BRIEF DESCRIPTION OF THE DRAWINGS ofthe downhole portion of the wellpumping system of FIG. 1 taken along line 3-3 of FIG. 2 illustrating theplunger of the pumping system on its downstro-ke with FIG. 3arepresenting the upper half of the downhole pumping system and FIG. 3brepresenting the lower half of the downhole pumping system.

FIGS. 4a and 4b correspond, respectively, to FIGS. 3a and 3b butillustrate the operation of the pumping system when the plunger is onits upstroke;

fluid in the form of high viscosity crude oil-impurity 'mixture 19 islocated. Such high viscosity crude oil 19 which is generally laden withsand and silt is commonly encountered in oil drilling operations in theSanta Maria, California region. Due to the sand and other impuritiesgenerally found in this crude oil 19, the oil 19 is generally of ahighly offensive nature, being abrasive and erosive and sometimescontaining corrosive salt water. The tubing string 15 provides a fluidsealed housing for a string of sucker rods 21 which are connected in aconventional manner to a prime mover 23, illustrated in FIG. 1 as apumping jack, which is mounted at well surface adjacent the well bore13. It is noted that the string of sucker rods 21 and the pumpingmechanism associated with the pumping system 11 may be driven by meansother than a pumping jack, such as, an appropriately adapted hydraulicengine, electric motor, gas expansion engine, etc. The tubing string 17functions as a string of production tubing and defines means forisolating pumped crude oil from the well reservoir and conducting thecrude oil 19 to the well surface, In this manner of employing tubingstrings 15 and 17, the sucker rod'string 21 is isolated from the wellfluid 19 so that rod fall is not restricted thereby and rod fall cyclerates as high as ten strokes per minute may be employed for pumping wellfluid to well surface. Such rod fall. rates of ten strokes per minutemay develop pumping pressures as high as 6,0007,000 pounds per squareinch without placing undue stress on the sucker rod string 21 which isisolated out of contact with the well fluid 19.

Mounted on the lower end of the tubing string 15 by means of a coupler25 is a conduit section 27 having a hollow side extension portion 29.The conduit section 27 with its extension 29 defines a first cavity orchamber 31. The cavity 31 is shaped to have a cylindrical portion inline with the vertically extending string of sucker rods 21 whichdefines a plunger chamber. A

plunger 33 is mounted in this plunger chamber for re- .ciprocation upand down therein. The plunger 33 forms amovable wall portion of thechamber 31 and functions when moved upward by the sucker rod string 21to decrease or contract the effective volume of the chamber 31.Conversely, downward movement of the sucker rod string 21 moves theplunger 33 downward to increase or expand the effective volume of thechamber 31. The chamber 31 which is made up of the region defining theplunger chamber and also the region enclosed by the side extension 29 isshown in FIGS. 3a and 4a. H

Connected by a coupler 35 to the lower end of the conduit section 27 isa conduit section 37 which opens on its upper end into the conduitsection 27. The conduit section 37 provides the fixed housing in whichthe plunger mechanism or assembly 33 reciprocates up and down. Atraveling valve 39 is connected to the plunger mechanism 33 toreciprocate therewith and the valve 39 which is preferably of the ballvalve type operates to control the flow of a displacing fluid 41 in amanner hereinafter explained to the chamber 31. The displacing fluid 41is of an inoffensive nature and preferably is kerosene or naptha blendedwith crude oil. The term inoffensive fluid" as used herein means a fluidwhich does not attack or unduly cause wear on pump parts on contact. Theinoffensive fluid may be lubricating, as kerosene, could be filteredcrude oil, could be a solvent for dissolving paraffin which hasprecipitated out of the displaced well fluid 19 onto pump parts, or anyother suitable fluid the contact of which with pump parts is notconsidered undesirable. A tubular cap 43 is mounted on the lower end ofthe conduit section 37 by means ofa coupler 45 to collect and provide areservoir for the displacing fluid 41. As shown in FIGS. 3a, 3b, 4a and4b, the sucker rods 21 are formed to be hollow and the displacing fluid41 is supplied by a fluid supply means 47 shown in FIG. 1 located atwell surface adjacent the well bore 13. The fluid supply 47 operates ina conventional manner to supply the displacing fluid 41 at a controlledrate through the conduit 49 to the upper end of the hollow sucker rods21. As indicated by the directional arrows in FIGS. 3a, 3b and 4a, 4b,the displacing fluid 41 flows down the sucker rods 21 out an exitportion 51 down the side of the conduit section 37 into the tubular cap43 where'at it is collected. The traveling valve 39 functions to controlthe, flow of the displacing fluid 41 upward through a channel 53 whichopens through the plunger mechanism 33 into the chamber 31. The chamber31 is a fluid confining chamber which functions to hold and confine themovement of this displacing fluid 41.

Formed integral with the side extension 29 of the conduit section 27 isa preferably tubular vertically disposed conduit section 55. The conduitsection 55 com municates with the chamber 31 and defines a downwardextending passage 56 which communicates at its lower end with a secondchamber 57 formed by a conduit section 59 branching off from the bottomportion of the conduit section 55 to extend upward therefrom. Theconduit sections 55 and 59 which are preferably formed as one integralunit form a generally U-shaped junction. Connected on the lower end ofthe conduit section 55 is a standing valve 61 which is preferably of theball valve type and has an inlet port 63 connected to its lower end. Thestanding valve 61 in combination with the inlet port 63 provides aninlet port means which functions as is hereinafter explained to permitthe flow of fluid, and in particular the flow of well fluid, only intobut not out from the chamber 57. The valve 61 acts as a check valve toprevent fluid flow therethrough out from the chamber 57. It is notedthat the term fluid, as here used, isused in a broad generic sense toencompass all types of fluent substances including slurries, such aspercent crude oil-6O percent sand slurry which may make up an oil wellreservoir. Connected to the upper end of the conduit section 59 is astanding valve 65 mounted in a coupler 67. The coupler 67 is connectedto the lower end of the tubing string 17 and the tubing string 17functions, as beforementioned. as a production tubing string forconducting pumped well fluid to the surface of the well while isolatingthe well fluid pumped from the sucker rod string and well reservoir. [tis noted that the tubing string 17 has no internal restrictions exceptits outer boundary. The standing valve 65 functions as an outlet portmeans for the chamber 57 through which pumped 'well fluid 19 isdischarged at a discharge point into the production tubing string 17 andacts to check the flow of any fluid into the chamber 57 therethrough.

The conduit section 55 extends vertically slightly above the extension29 to form a gas trap chamber 69. The upper end of the conduit section55 has a coupler 71 with a standing valve 73, preferably of the ballvalve type, mounted therein. The valve 73 functions to bleed trapped gasfrom the gas trap chamber 69 into an upper gas reservoir chamber 75defined by a tubular cap 77 connected to the coupler 71. Connected tothe upper end of the gas reservoir chamber 75 is a conduit 81 by meansof a right angled elbow connector 79. The conduit 81 extends downwardfrom the connector 79 to a point adjacent the upper portion of thestructurally defined chamber 57 at which it is connected to a standingvalve 83. The valve 83 is preferably of the ball valve type and isspring biased in a closed position. An outlet conduit 85 is connectedfrom the ball valve assembly 83 in fluid sealing relation through onewall of the chamber 57 to direct gas therefrom into the upward extendingportion of the conduit section 59. Thereby, the gas is pumped throughthe standing valve 65 with well fluid 19 into the string of productiontubing 17. It is noted that screen strainers 87 and 89 are mounted afterand before, respectively, the valves 73 and 83 to strain particles outof the gas flow so as to prevent the clogging of the elbow connector 79,the conduit 81, the valve assembly 83 or the conduit 85. Further, it isnoted that the construction of the valve 73 is designed with its orificerelatively small so that, should gas not be evolved from the well fluid19 being pumped, only negligible displacing fluid 41 will flow throughthe valve 73 and into the gas elimination system or assembly provided bythe gas trap 69, the valves 73 and 83, the reservoir chamber 75, theconnector 79, and the conduits 81 and 85.

In operation of the exemplary well pumping system shown in FIGS. 1-7,initially the lubricating fluid kerosene 41 is supplied to flood thepump chambers 31, 57 and the passage 56. Prime mover 23 is thenenergized and acts to reciprocate the sucker rod string 21 up and down.Thereby, the plunger 33 is driven to move up and down and change theeffectivevolume of the chamber 31 so that well fluid 19 is drawn intothe chamber 57 and a fluid interface is formed in the upwardly extendingchannel or interface chamber formed bly 39 is opened by the pressure ofdisplacing fluid 41 in the reservoir defined by the cap 43 so thatdisplacing fluid 41 flows upward through the valve assembly 39 .into thecavity 31. Also during the downstroke of the plunger 33, a low pressureregion is formed in the chamber 57 so that the pressure of the wellfluid 19in the bottom of well bore 13 opens the standing valve 61 andthe well fluid 19 to be pumped which is a crude oilimpurityfluentmixture flows into the chamber 57. This flow of fluid 19 into thechamber 57 forces the interface region 91 upward in the passage 56 andthe displacing fluid kerosene 41 tends to flow into the expandingchamber 31, as indicated by the directional arrows in FIGS. 30 and 3b.Additionally, gas evolved from the oil 19 being pumped flows up thevertical path defined by the conduit section 55 into the gas trap 69 andforces the gas-displacing fluid interface 93 in a downward direction, asindicated by the directional arrows, during the downstroke of theplunger 33. It is noted that the valve assembly 73 is closed by thepressure dif' ferential thereacross during the downstroke of the plunger33. Additionally during the plunger downstroke, the outlet port definedby the valve assembly 65 is closed since the displacing fluid interface91 is moving upwards at this time in the passage 56.

FIGS. 40 and 4b show the upstroke of the plunger 33.

In the upstroke, the plunger 33 functions to contract placing fluid 41defined in the cap 43, the valve assembly 39 is closed by the pressuredifferential thereacross. The downward movement of the displacingkerosene 41 in the conduit section 55 functions to move the interfaceregion 91 downward in a piston-like movement in the passage 56 so thatthe well fluid 19 is forced downward toward Ihechamber 57. This downwardmovement of the displaced fluid 19 in the chamber 57 automaticallycloses the inlet valve means 61 and opens the outlet valve means 65 sothat the crude oil 19 is channeled and pumped into the production tubingstring 17 upward to the surface of the well. The upward movement of thedisplacing fluid 41 in the conduit sec tion 55 functionsto increase thepressure of the gas in the gas trap 69 so that the valve 73 opens andthe evolved gas flows into the gas reservoir 75. The gas stored in thegas reservoir 75 is thus put under an increased pressure and flows downthe conduit 81 to open the spring-biased valve 83. The opening of thespring-biased valve 83 bleeds'off the gas in the conduit 81 down to apredetermined pressure level established by the spring-biased valve 83.This bled off gas is discharged into the upward extending portion of theconduit section 59 where it is pumped with the well fluid 19 into theproduction tubing string 17 out of the well. It is noted that gas isnormally only forced through the gas elimination assembly during theupstroke of the plunger 33 when the chamber 31 is being contracted toits smallest effective volume and at which time the displacing fluid 41is exerting maximum pressure against gas in the gas trap 69.

Operation of the 'prime mover 23, thus, functions to pump oil or wellfluid 19 up the production tubing 17 in a rapid and efficient mannersince no moving parts other than the inlet and outlet ports defined byvalves 61 and 65 of the pumpassembly contact the offensive crude oil 19being pumped. Further, the prime mover 23 may be driven at a relativelyhigh cycle rate since the sucker rod string 21 is siolated from contactwith the well fluid 19 so that even high viscosity fluids such as oil ofthe type recovered from Santa Maria, California, can be rapidly pumpedup the production tubing 17. Also, kerosene or another light lubricatingfluid is preferably maintained within the tubing 15 around the suckerrod string 21 which is operable to lubricate the sucker rod string 21without restricting the rate of rod fall. This kerosene may be suppliedfrom the supply means 47.

Referring now to FIG. 8, a modified form of the pumping system of FIGS.1 to 7 is shown therein in which a downward extending fluid injectionsystem is included. The system 95 has a conduit 97 with a spring-biasedvalve assembly 99 mounted on the lower end of the conduit 97 and aconnector 101 connecting the upper end of the conduit 97 to the tubing15. A diluent injection assembly is, thus, provided in which a diluentfluid which may be kerosene is pumped down the tubing string 15 throughthe connector 101 and the conduit 97'and is injected into the well fluid19 at a rate controlled by the spring-biased valve 99 through a nozzleor orifice means 103 connected to the valve 99. The flow of the diluentfluid is shown by directional arrows in FIG. 8. Thereby, the well fluid19 is diluted to reduce its viscosity before being pumped into thechamber 57 and discharged therefrom into the production tubing 17. It isalso noted that by pumping a lubricating fluid, such as kerosene, downthe tubing string 15 external of the sucker string 21 that a lubricantis automatically provided for the reciprocating sucker string 21 whichdoes not restrict rod fall. The diluent may be supplied by the fluidsupply means 47 or by another conventional source.

lt is noted that the exemplary pump has been tested and may be used withor without the above-described gas elimination section connectedthereto. For example, the gas elimination assembly has not been foundnecessary when using the exemplary pump to pump a crude oil-impurityfluent mixture having'an inherently low gas-oil ratio. Further, it isnoted that means may be provided so that the pump is designed to pumpboth on the upstroke and the downstroke of its plunger mechanism 33 andthat while the pump structure provided by the conduits 27, 37, 55 and 59is illustrated connected onto the ends of the tubing strings 15 and 17in a downhole pumping operation that a pump mechanism operated on thesame principle could be used in other pumping operations as well. Themeans for expanding and contracting the chamber 31 could take the formof other suitable arrangements or means other than a plunger and couldbe driven by a downhole motor instead of a surface mounted prime mover.Additionally, other equivalent type valving arrangements, such as poppetvalves, could be employed in place of the ball type valves and theentire lower end of the pump structure could be made the inlet means tofacilitate the pumping in of extremely high viscosity fluent mixturesinto the pump structure, such as a 60 percent sand-40 percent crude oilmixture. Also, instead of using a production tubing string to conductthe pumped well fluid 19 to well surface, a seal could be placed in the.well bore 13 to seal off the discharge point of the pumps outlet portfrom the well reservoir so that the well bore or casing 13 could beutilized as a conduit to conduct the well fluid to well surface.

Further, it is noted that instead of pumping the displacing fluid downthe sucker rods that solid, less expensive sucker rods could be usedwith other conventional means for conducting the displacing fluid intothe chamber 31. Also, the displacing fluid 41 need be supplied to thechamber 3 1 only at a rate necessary to replace displacing fluid lostduring the operation of pumping the well fluid up the production tubing17, thereby to maintain the displacing fluid-well fluid interfaceestablished in the passage 56. In the case of using kerosene to pump oilthe displacing fluid kerosene needs to be supplied, for example, at therate of 10 percent of the pumps displacement. Additionally whilekerosene is illustrated as the displacing fluid, it is noted that othersuitable fluid which are of an inoffensive nature so as to not attack orcause undue wear of the pumping mechanism could be employed, such aswater and various other suitable fluids. Filtered oil, for example,could be used to pump a crude oil-impurity mixture from a wellreservoir. Further, it is noted that the displacing fluid kerosene ismiscible with the well fluid crude oil and that by keeping a movinginterface between the fluids that little displacing fluid is mixed withthe crude oil pumped up the production tubing 17. While the downholepumping system is utilized to pump crude oil it is to be understood thatother fluidlike substances having high percentages of impurities andbeing extremely abrasive and/or corrosive could also be pumped by thispumping mechanism, such as mud, The pump could also be employed as anacid pump by employing as the displacing fluid an inoffensive fluidinert to the fluid being pumped to pump a high corrosive acid, such as,anhydrous sulfuric acid.

Although I have herein shown and described my invention in what I haveconceived to be the most practical and preferred embodiment, it isrecognized that departures may be made therefrom within the scope of myinvention.

1 claim:

1. In a down hole well pumping system, the improvement comprising:

pump structure for positioning in a well bore down hole in contact witha well reservoir, said pump structure defining a first fluid confiningchamber for receiving displacing fluid, a second fluid confin-- ingchamber for receiving well fluid and a fluid conducting passageinterconnecting said fluid confining chambers in communication with eachother, said second chamber having an inlet and outlet port definedtherein, said inlet port being defined to communicate with the wellreservoir in which said pump structure is positioned, said passageextending upwardly from its point of communication with said secondchamber to define an upwardly extending channel of predetermined lengthin which displacing fluid and well fluid may interface, at least aportion of said first chamber defining a plunger chamber; inlet valvemeans mounted in said inlet port for conducting well fluid into saidsecond chamber; outlet valve means mounted in said outlet port fordischarging fluid from said second chamber; means for expanding andcontracting the effective volume of said first chamber, each expansionand contraction of the effective volume of said first chamber beingdefined as a pump stroke, said means for expanding and contracting theeffective volume of said first chamber being a plunger means mounted forreciprocal motion in said plunger chamber;

means for supplying displacing fluid to said pump structure on eachstroke of said pump at a controllable rate to maintain the movinginterface region between displacing fluid and well fluid within saidupwardly extending channel and said second chamber, said displacingfluid supply means being operable to supply displacing fluid to saidpump structure in time coincidence with the expansion of the effectivevolume of said first chamber;

said displacing fluid supply means comprising: reservoir means fordisplacing fluid defined as a continuation of said plunger chamber, saidplunger means sealing said first chamber from said reservoir meanswhereby movement of said plunger means to contract and expand theeffective volume of said first chamber, respectively, expands andcontracts the volume of said reservoir means; means connected to saidreservoir means for transferring displacing fluid thereto at acontrolled rate; and valve means mounted in said plunger means forcontrolling the flow of displacing fluid between said reservoir meansand said first chamber, said valve means being operated by the pressuredifferential developed between said first chamber and said reservoirmeans to open and close, respectively, during the expansion andcontraction of the effective volume of said first chamber; and

means for conducting fluid pumped from said outlet valve means to wellsurface.

2. In a down hole well pumping system, the improvement comprising:

pump structure for positioning in a well bore down hole in contact witha well reservoir, said pump structure defining a first fluid confiningchamber for receiving displacing fluid, a second fluid confining chamberfor receiving well fluid and a fluid conducting passage interconnectingsaid fluid confining chambersin communication with each other, saidsecond chamber having an inlet and outlet port defined therein, saidinlet port being defined to communicate with the Well reservoir in whichsaid pump structure is positioned, said passage extending upwardly fromits point of communication with said second chamber to define anupwardly extending channel of predetermined length in which displacingfluid and well fluid may interface, at least a portion of said firstchamber defining a vertically extending plunger chamber;

inlet valve means mounted in said inlet port for conducting well fluidinto said second chamber;

outlet valve means mounted in said outlet port for discharging fluidfrom said second chamber;

means for expanding and contracting the effective volume of said firstchamber, said means for expanding and contracting the effective volumeof said first chamber is a plunger means mounted for up and downreciprocal motion in said plunger chamber;

means for supplying displacing fluid to said pump structure at acontrollable rate to maintain the moving interface region betweendisplacing fluid and well fluid within said upwardly extending chanvoirmeans for displacing fluid defined as a continuation of said plungerchamber, said plunger chamber being positioned above said reservoirmeans, said plunger means sealing said first chamber from said reservoirmeans whereby movement of said plunger means to contract and expand theeffective volume of said first chamber, respectively, expands andcontracts the volume of said reservoir means; means connected to saidreservoir means for transferring displacing fluid thereto at acontrolled rate; and valve means mounted in said plunger means forcontrolling the flow of displacing fluid between said reservoir meansand said first chamber, said valve means being operated by the pressurediffer ential developed betweensaid first chamber and said reservoirmeans to open and close, respectively, during the expansion andcontraction of the effectivevolume of said first chamber; and means forconducting fluid pumped from said outlet valve means to well surface. 3.The invention defined in claim 2, including a string of suckerrods forreciprocating said plunger means up and down, said sucker rods beingconnected to said plunger means and extending therefrom to well surface,said sucker rods being hollow and defining a conduit for conductingdisplacing fluid from well surface to said plunger means, said plungermeans having a fluid conducting path defined therethrough for conductingdisplacing fluid from said sucker rods to said reservoir means.

4. A well pumping system, comprising:

a sucker rod string;

a fluid sealed string of tubing for positioning in a well to extend fromthe bottom portion ofa well to well surface, said sucker rod stringbeing mounted in said string of tubing for reciprocation up and downtherein whereby said tubing functions as a housing to isolate saidsucker rod string from well fluid thereby up and down reciprocalmovement of said sucker rod string is not inhibited by well fluid;

pump structure mounted on the lower end of said string of tubing todepend therefrom into the reservoir of ,well fluid to be pumped, saidpump structure defining a first fluid confining chamber in communicationwith a second fluid confining chamber through a fluid conductingpassage, said first and second chambers being for holding, respectively,a displacing fluid and a well fluid, said passage extending upwardlyfrom its point of communication with said second chamber to define anupwardly extending channel in which displacing fluid and well fluid mayinterface, said second chamber having inlet and outlet port meansoperable only to receive and discharge fluid, respectively; g

1 plunger means mounted for up and down reciprocal motion in said firstchamber for expanding and contracting the effective volume of said firstcham ber to displace up and down in said channel the region of interfacebetween the displacing fluid and the well fluid whereby the displacingfluid functions as a piston to pump well fluid in said inlet port meansand out said discharge, port means;

means for isolating the dischargepoint of said outlet port means of saidpump structure from the well fluid reservoir and connecting said outletport means in communication with well surface so that well fluiddischarged from said outlet port means is pumped to well surface;

means for connecting said plunger means to said sucker rod stringwhereby said plunger means may be driven through said sucker rod string;

displacing fluid supply means connected to said first chamber forsupplying displacing fluid thereto at a controllable rate to maintainthe moving region of interface between the displacing fluid and the wellfluid within said upwardly extending channel and said second chamber,said displacing fluid. supply means being operable to supply displacingfluid to said pump structure in time coincidence with the expansion ofthe effective volume of said first chamber;

said displacing fluid supply means comprising: structure defining areservoir for displacing fluid, said displacing fluid reservoir beingdefined by a downwardly extending continuation of said first chamber andbeing in alignment with 'said plunger means; means connected to saiddispiacing fluid reservoir for transferring displacing fluid thereto ata controlled rate; and valve means connecting said displacing fluidreservoir in communication with said first chamber for controlling theflow of displacing fluid between said displacing fluid reservoir andsaid first chamber, said valve means being 0perable to open and close,respectively, in time coincidence with the expansion and contraction ofthe effective volume of said first chamber, said valve means beingoperated by the pressure differential developed between said firstchamber and said displacing fluid reservoir during the expansion andcontraction of the effective volume of said first chamber;

said plunger means scaling said first chamber from said displacing fluidreservoir whereby the up and down reciprocal movement of said plungermeans to contract and expand the effective volume of said first chamber,respectively, expands and contracts the volume of said reservoir means,said valve means being carried by said plunger means; and

prime mover means connected to said sucker rod string for driving saidsucker rod string in up and down reciprocal motion thereby to drive saidplunger means.

5. The invention defined in claim 4, wherein:

said sucker rods are hollow and define a conduit for conductingdisplacing fluid from well surface to said plunger means; and

said plunger means has a fluid conducting path defined therethrough forconducting displacing fluid from said sucker rods to said displacingfluid reservoir.

6. The invention defined in claim 4, wherein said means for isolatingthe discharge point of said outlet port means of said pump structurefrom the well fluid reservoir and connecting said outlet port means incommunication with well surface is a string of production tubingdetachably coupled to said outlet port means.

7. The invention defined in claim 4, wherein:

said sucker rod string defines a conduit for conducting displacing fluidfrom well surface to said plunger means; and

said plunger means has a fluid conducting path defined therethrough forconducting displacing fluid from said sucker rod string to saidreservoir means.

8. The invention defined in claim 7, wherein said means for isolatingthe discharge point of said outlet port means of said pump structurefrom the well fluid reservoir and connecting said outlet port means incommunication with well surface is a string of production tubingdetachably coupled to said outlet port means.

9. A pump for down hole use, comprising:

structure defining a first fluid confining chamber for receivingdisplacing fluid, a second fluid confining chamber for receiving wellfluid and a fluid conducting passage interconnecting said fluidconfining chambers in communication with each other, said second chamberhaving an' inlet and outlet port defined therein, said inlet port beingdefined to communicate with a well reservoir, said passage extendingupwardly from its point of communication with said second chamber todefine an upwardly extending channel of predetermined length in whichdisplacing fluid and well fluid may interface, at least a portion ofsaid first chamber defining a plunger chamber;

inlet valve means mounted in said inlet port for conducting well fluid into said second chamber; outlet valve means mounted insaid outlet portfor discharging'fluid from said second chamber; reservoir means definedas a continuation of said plunger chamber, said reservoir means beingarranged for connection to a displacing fluid supply so that displacingfluid may be selectively supplied thereto;

plunger means mounted for reciprocal motion in said plunger chamber forexpanding and contracting the effective volume of said first chamber,said plunger means sealing said first chamber from said reservoir meanswhereby movement of said plunger means to contract and expand theeffective volume of said first chamber, respectively, expands andcontracts the volume of said reservoir means;

and

valve means mounted in said plunger means for controlling the flow ofdisplacing fluid between said reservoir means and said first chamber,said valve means being operated by the pressure differential developedbetween said first chamber and reservoir means to open and close,respectively, during the expansion and contraction of the effectivevolume of said first chamber.

10. The invention defined in claim 9, wherein:

said plunger chamber is defined to be substantially verticallyextending; and

said reservoir means is defined as a downward continuation of saidplunger chamber.

11. The invention defined in claim 10, wherein:

said plunger means is arranged for connection to a string of upwardlyextending hollow sucker rods whereby sand plunger means may be driven upand down and displacing fluid may be conducted from well surface to saidplunger means through a string of hollow sucker rods connected thereto;and said plunger means has a fluid conducting path defined therethroughfor conducting displacing fluid to said reservoir means from the pointof connection of a string of hollow sucker rods thereto.

12. The invention defined in claim 11, wherein said outlet port isarranged for being detachably coupled to a string of production tubing.

13. The invention defined in claim 9, wherein said outlet port isarranged for being detachably coupled to a string of production tubing.

14. A pump for downhole use to pump well fluid from a well, said pumpcomprising:

structure defining a first fluid confining chamber in communication witha second fluid confining chamber through a fluid conducting passage,said first and second chambers being for holding, respectively, adisplacing fluid and a well fluid, said passage extending upwardly fromits point of communication with said second chamber to define anupwardly extending channel in which displacing fluid and well fluid mayinterface, said second chamber having inlet and outlet port meansoperable only to receive and discharge fluid, respectively, said pumpstructure having a gas trap defined therein above and in communicationwith the upper end of said channel to trap gas evolved from 1 the wellfluid, and including valve controlled conduit means connected forconducting trapped gas from said gas trap to a point in said secondchamber adjacent said outlet port means so that the gas is pumped out ofsaid second chamber with well fluid, said valve controlled conduit meansbeing operable to control the flow of gas therethrough as a function ofthe pressure level of gas being conducted therethrough and the pressurelevels within said gas trap and said second chamber;

means for injecting displacing fluid at a controlled rate into saidfirst chamber, said means arranged for connection to a source ofdisplacing fluid;

means for expanding and contracting the effective volume of said firstchamber to displace up and down in said'channel the region of interfacebetween the displacing fluid and the well fluid whereby the displacingfluid functions as a piston to pump well fluid in said inlet port meansandout said discharge port means, said means being constructed forconnection with a prime mover; and

means for conducting. fluid pumped from said outlet port means to wellsurface.

15. The invention recited in claim 14, wherein said inlet port meansincludes a check valve operative to prevent fluid flow therethrough outfrom said second chamber and said 'outlet port means includes a checkvalve operative to prevent fluid flow therethrough into said secondchamber.

16. The invention recited in claim 14, including means for supplyingdisplacing fluid, said displacing fluid supply means being connected tosaid fluid injecting means to maintain the region of interface betweenthe displacing fluid and the displaced fluid within said channel andsecond chamber.

17. The invention recited in claim 14, wherein said means for expandingand contracting the effective volume of said first chamber is a plungermeans mounted therein for up and down reciprocal motion, said plungermeans being adapted for connection through a string of sucker rods to aprime mover.

18. The invention recited in claim 14, including fluid injection meansassociated with said structure to extend into well fluid being pumpedfor injecting controlled quantities of a diluent fluid into the wellfluid to be pumped whereby to dilute and thereby reduce the viscosity ofthe well fluid.

19. The invention recited in claim 14, wherein said means for expandingand contracting the effective volume of said first chamber is a plungermeans mounted therein for reciprocal motion.

20. The invention recited in claim 19, including prime mover meansconnected to said plunger means for driving said plunger means in itsreciprocal path of motion. I

21. A well pumping system, comprising:

a sucker rod string;

a fluid sealed string of tubing for positioning in a well to extend fromthe bottom portion of a well to well surface, said sucker rod stringbeing mounted in said string of tubing for reciprocation up and downtherein whereby said tubing functions as a housing to isolate saidsucker rod string from well fluid thereby up and down reciprocalmovement of said sucker rod string is not inhibited by well fluid;

pump structure mounted on the lower end of said string of tubing todepend therefrom into the reservoir of well fluid to be pumped, saidpump structure defining a first fluid confining chamber in communicationwith a second fluid confining chamber through a fluid conductingpassage, said first and second chambers being for holding, respectively,a displacing fluid and a well fluid, said passageextending upwardly fromits point of communication with said second chamber to define anupwardly extendingchannel in which displacing fluid and well fluid mayinterface, said second chamber having inlet and outlet port meansoperable only to receive and discharge fluid, respectively, said pumpstructure having a gas trap defined therein above and in communicationwith the upper end of said channel to trap gas evolved from the 'wellfluid, and including valve controlled conduit means connected forconducting trapped gas from said gas trap to a point in said secondchamber adjacent said outlet-port means so that the gas is pumped out ofsaid second chamber with well fluid, said valve controlled conduit meansbeing operable to control the flow of gas therethrough as 7 a functionof the pressure level of gas being conducted therethrough and thepressure levels within said gas trap and said second chamber;

plunger means mounted for up and down reciprocal motion in said firstchamber for expanding and contracting the effective volume of said firstchamher to displace up and down in said channel the region of interfacebetween the displacing fluid and the well fluid whereby the displacingfluid functions as a piston to pump well fluid in said inlet port meansand out said outlet port means;

means for isolating the discharge point of said outlet port means ofsaid pump structure from the well fluid reservoir and connecting saidoutlet port means in communication with well surface so that well fluiddischarged from said outlet port means is pumped to well surface;

means for connecting said plunger means to said sucker rod stringwhereby said plunger means may be driven through said sucker rod string;displacing fluid supply means connected to said first chamber forsupplying displacing fluid thereto at a controllable rate to'maintainthe moving region of interface'between the displacing fluid and the wellfluid within said upwardly extending channel and said second chamber;and prime mover means connected to said sucker rod string for drivingsaid sucker rod string in up and down reciprocal motion thereby to drivesaid plunger means.

22. The invention recited in claim 21, wherein the well fluid is of anoffensive nature and the displacing fluid is of an inoffensive nature.

23. The invention defined in claim 21, including lubricating fluidwithin said fluid sealed string of tubing to provide a lubricated paththrough which said sucker rod string may reciprocate with minimum wearand substantially free fall velocity.

crude oil being pumped for injecting controlled quanti- I ties ofa'diluent fluid into the high viscosity crude oil wherebyto dilute thecrude oil and reduce its viscosity.

25. The invention recited in claim 24, wherein the diluent fluid iskerosene.

26. The invention defined in claim 21, wherein said means for isolatingthe discharge point of said outlet port means from thewell fluidreservoir and connecting said outlet port means in communication withwell surface is a fluid sealed string of production tubing.

27. The invention defined in claim 26, wherein said string of productiontubing is detachably coupled to said pump structure.

28. The invention defined in claim 21, wherein said displacing fluidsupply means is operable to supply displacing fluid to said pumpstructure in time coincidence with the expansion of the effective volumeof said first chamber.

29. The invention defined in claim 28, wherein said displacing fluidsupply means comprises:

structuredefining a reservoir for displacing fluid;

means connected to said displacing fluid reservoir for transferringdisplacing fluid thereto at a controlled rate; and I valve meansconnecting said displacing fluid reservoir in communication with saidfirst chamber for controlling the flow of displacing fluid between saiddisplacing fluid reservoir and said first chamber, said valve meansbeing operable to open and close, respectively, in time coincidence withthe expansion and contraction of the effective volume of said firstchamber. a

30. The invention defined in claim 29, wherein said valve means isoperated by the pressure differential developed between said firstchamber and said displacing fluid reservoir during the expansion andcontraction of the effective volume of said first chamber.

31. The invention defined in claim 30, wherein:

said displacing fluid reservoir is defined by a downwardly extendingcontinuation of said first cham- 17 a 18 her, said displacing fluidreservoir being in aligncontract and expand the effective volume of saidment with said plunger means; and first chamber, respectively, expandsand contracts said plunger means seals said first chamber from said thevolume of said reservoir means; and

displacing fluid reservoir whereby the up and down said valve means iscarried by said plunger means. reciprocal movement of said plunger meansto

1. In a down hole well pumping system, the improvement comprising: pumpstructure for positioning in a well bore down hole in contact with awell reservoir, said pump structure defining a first fluid confiningchamber for receiving displacing fluid, a second fluid confining chamberfor receiving well fluid and a fluid conducting passage interconnectingsaid fluid confining chambers in communication with each other, saidsecond chamber having an inlet and outlet port defined therein, saidinlet port being defined to communicate with the well reservoir in whichsaid pump structure is positioned, said passage extending upwardly fromits point of communication with said second chamber to define anupwardly extending channel of predetermined length in which displacingfluid and well fluid may interface, at least a portion of said firstcHamber defining a plunger chamber; inlet valve means mounted in saidinlet port for conducting well fluid into said second chamber; outletvalve means mounted in said outlet port for discharging fluid from saidsecond chamber; means for expanding and contracting the effective volumeof said first chamber, each expansion and contraction of the effectivevolume of said first chamber being defined as a pump stroke, said meansfor expanding and contracting the effective volume of said first chamberbeing a plunger means mounted for reciprocal motion in said plungerchamber; means for supplying displacing fluid to said pump structure oneach stroke of said pump at a controllable rate to maintain the movinginterface region between displacing fluid and well fluid within saidupwardly extending channel and said second chamber, said displacingfluid supply means being operable to supply displacing fluid to saidpump structure in time coincidence with the expansion of the effectivevolume of said first chamber; said displacing fluid supply meanscomprising: reservoir means for displacing fluid defined as acontinuation of said plunger chamber, said plunger means sealing saidfirst chamber from said reservoir means whereby movement of said plungermeans to contract and expand the effective volume of said first chamber,respectively, expands and contracts the volume of said reservoir means;means connected to said reservoir means for transferring displacingfluid thereto at a controlled rate; and valve means mounted in saidplunger means for controlling the flow of displacing fluid between saidreservoir means and said first chamber, said valve means being operatedby the pressure differential developed between said first chamber andsaid reservoir means to open and close, respectively, during theexpansion and contraction of the effective volume of said first chamber;and means for conducting fluid pumped from said outlet valve means towell surface.
 2. In a down hole well pumping system, the improvementcomprising: pump structure for positioning in a well bore down hole incontact with a well reservoir, said pump structure defining a firstfluid confining chamber for receiving displacing fluid, a second fluidconfining chamber for receiving well fluid and a fluid conductingpassage interconnecting said fluid confining chambers in communicationwith each other, said second chamber having an inlet and outlet portdefined therein, said inlet port being defined to communicate with thewell reservoir in which said pump structure is positioned, said passageextending upwardly from its point of communication with said secondchamber to define an upwardly extending channel of predetermined lengthin which displacing fluid and well fluid may interface, at least aportion of said first chamber defining a vertically extending plungerchamber; inlet valve means mounted in said inlet port for conductingwell fluid into said second chamber; outlet valve means mounted in saidoutlet port for discharging fluid from said second chamber; means forexpanding and contracting the effective volume of said first chamber,said means for expanding and contracting the effective volume of saidfirst chamber is a plunger means mounted for up and down reciprocalmotion in said plunger chamber; means for supplying displacing fluid tosaid pump structure at a controllable rate to maintain the movinginterface region between displacing fluid and well fluid within saidupwardly extending channel and said second chamber, said displacingfluid supply means being operable to supply displacing fluid to saidpump structure in time coincidence with the expansion of the effectivevolume of said first chamber; said displacing fluid supply meanscomprising: reservoir means for displacing fluid defined as acontinuation of said plunger chamber, said plunger chamber beingpositioned above said reservoir means, said plunger means sealing saidfirst chamber from said reservoir means whereby movement of said plungermeans to contract and expand the effective volume of said first chamber,respectively, expands and contracts the volume of said reservoir means;means connected to said reservoir means for transferring displacingfluid thereto at a controlled rate; and valve means mounted in saidplunger means for controlling the flow of displacing fluid between saidreservoir means and said first chamber, said valve means being operatedby the pressure differential developed between said first chamber andsaid reservoir means to open and close, respectively, during theexpansion and contraction of the effective volume of said first chamber;and means for conducting fluid pumped from said outlet valve means towell surface.
 3. The invention defined in claim 2, including a string ofsucker rods for reciprocating said plunger means up and down, saidsucker rods being connected to said plunger means and extendingtherefrom to well surface, said sucker rods being hollow and defining aconduit for conducting displacing fluid from well surface to saidplunger means, said plunger means having a fluid conducting path definedtherethrough for conducting displacing fluid from said sucker rods tosaid reservoir means.
 4. A well pumping system, comprising: a sucker rodstring; a fluid sealed string of tubing for positioning in a well toextend from the bottom portion of a well to well surface, said suckerrod string being mounted in said string of tubing for reciprocation upand down therein whereby said tubing functions as a housing to isolatesaid sucker rod string from well fluid thereby up and down reciprocalmovement of said sucker rod string is not inhibited by well fluid; pumpstructure mounted on the lower end of said string of tubing to dependtherefrom into the reservoir of well fluid to be pumped, said pumpstructure defining a first fluid confining chamber in communication witha second fluid confining chamber through a fluid conducting passage,said first and second chambers being for holding, respectively, adisplacing fluid and a well fluid, said passage extending upwardly fromits point of communication with said second chamber to define anupwardly extending channel in which displacing fluid and well fluid mayinterface, said second chamber having inlet and outlet port meansoperable only to receive and discharge fluid, respectively; plungermeans mounted for up and down reciprocal motion in said first chamberfor expanding and contracting the effective volume of said first chamberto displace up and down in said channel the region of interface betweenthe displacing fluid and the well fluid whereby the displacing fluidfunctions as a piston to pump well fluid in said inlet port means andout said discharge port means; means for isolating the discharge pointof said outlet port means of said pump structure from the well fluidreservoir and connecting said outlet port means in communication withwell surface so that well fluid discharged from said outlet port meansis pumped to well surface; means for connecting said plunger means tosaid sucker rod string whereby said plunger means may be driven throughsaid sucker rod string; displacing fluid supply means connected to saidfirst chamber for supplying displacing fluid thereto at a controllablerate to maintain the moving region of interface between the displacingfluid and the well fluid within said upwardly extending channel and saidsecond chamber, said displacing fluid supply means being operable tosupply displacing fluid to said pump structure in time coincidence withthe expansion of the effective volume of said first chamber; saiddisplacing fluid supply means comprising: structure defining a reservoirfor displacing fluid, said displacing fluid reservoir being defined by adownwardly extending continuation of said first chamber and being inalignment with said plunger means; means connected to said displacingfluid reservoir for Transferring displacing fluid thereto at acontrolled rate; and valve means connecting said displacing fluidreservoir in communication with said first chamber for controlling theflow of displacing fluid between said displacing fluid reservoir andsaid first chamber, said valve means being operable to open and close,respectively, in time coincidence with the expansion and contraction ofthe effective volume of said first chamber, said valve means beingoperated by the pressure differential developed between said firstchamber and said displacing fluid reservoir during the expansion andcontraction of the effective volume of said first chamber; said plungermeans sealing said first chamber from said displacing fluid reservoirwhereby the up and down reciprocal movement of said plunger means tocontract and expand the effective volume of said first chamber,respectively, expands and contracts the volume of said reservoir means,said valve means being carried by said plunger means; and prime movermeans connected to said sucker rod string for driving said sucker rodstring in up and down reciprocal motion thereby to drive said plungermeans.
 5. The invention defined in claim 4, wherein: said sucker rodsare hollow and define a conduit for conducting displacing fluid fromwell surface to said plunger means; and said plunger means has a fluidconducting path defined therethrough for conducting displacing fluidfrom said sucker rods to said displacing fluid reservoir.
 6. Theinvention defined in claim 4, wherein said means for isolating thedischarge point of said outlet port means of said pump structure fromthe well fluid reservoir and connecting said outlet port means incommunication with well surface is a string of production tubingdetachably coupled to said outlet port means.
 7. The invention definedin claim 4, wherein: said sucker rod string defines a conduit forconducting displacing fluid from well surface to said plunger means; andsaid plunger means has a fluid conducting path defined therethrough forconducting displacing fluid from said sucker rod string to saidreservoir means.
 8. The invention defined in claim 7, wherein said meansfor isolating the discharge point of said outlet port means of said pumpstructure from the well fluid reservoir and connecting said outlet portmeans in communication with well surface is a string of productiontubing detachably coupled to said outlet port means.
 9. A pump for downhole use, comprising: structure defining a first fluid confining chamberfor receiving displacing fluid, a second fluid confining chamber forreceiving well fluid and a fluid conducting passage interconnecting saidfluid confining chambers in communication with each other, said secondchamber having an inlet and outlet port defined therein, said inlet portbeing defined to communicate with a well reservoir, said passageextending upwardly from its point of communication with said secondchamber to define an upwardly extending channel of predetermined lengthin which displacing fluid and well fluid may interface, at least aportion of said first chamber defining a plunger chamber; inlet valvemeans mounted in said inlet port for conducting well fluid into saidsecond chamber; outlet valve means mounted in said outlet port fordischarging fluid from said second chamber; reservoir means defined as acontinuation of said plunger chamber, said reservoir means beingarranged for connection to a displacing fluid supply so that displacingfluid may be selectively supplied thereto; plunger means mounted forreciprocal motion in said plunger chamber for expanding and contractingthe effective volume of said first chamber, said plunger means sealingsaid first chamber from said reservoir means whereby movement of saidplunger means to contract and expand the effective volume of said firstchamber, respectively, expands and contracts the volume of saidreservoir means; and valve means moUnted in said plunger means forcontrolling the flow of displacing fluid between said reservoir meansand said first chamber, said valve means being operated by the pressuredifferential developed between said first chamber and reservoir means toopen and close, respectively, during the expansion and contraction ofthe effective volume of said first chamber.
 10. The invention defined inclaim 9, wherein: said plunger chamber is defined to be substantiallyvertically extending; and said reservoir means is defined as a downwardcontinuation of said plunger chamber.
 11. The invention defined in claim10, wherein: said plunger means is arranged for connection to a stringof upwardly extending hollow sucker rods whereby sand plunger means maybe driven up and down and displacing fluid may be conducted from wellsurface to said plunger means through a string of hollow sucker rodsconnected thereto; and said plunger means has a fluid conducting pathdefined therethrough for conducting displacing fluid to said reservoirmeans from the point of connection of a string of hollow sucker rodsthereto.
 12. The invention defined in claim 11, wherein said outlet portis arranged for being detachably coupled to a string of productiontubing.
 13. The invention defined in claim 9, wherein said outlet portis arranged for being detachably coupled to a string of productiontubing.
 14. A pump for downhole use to pump well fluid from a well, saidpump comprising: structure defining a first fluid confining chamber incommunication with a second fluid confining chamber through a fluidconducting passage, said first and second chambers being for holding,respectively, a displacing fluid and a well fluid, said passageextending upwardly from its point of communication with said secondchamber to define an upwardly extending channel in which displacingfluid and well fluid may interface, said second chamber having inlet andoutlet port means operable only to receive and discharge fluid,respectively, said pump structure having a gas trap defined thereinabove and in communication with the upper end of said channel to trapgas evolved from the well fluid, and including valve controlled conduitmeans connected for conducting trapped gas from said gas trap to a pointin said second chamber adjacent said outlet port means so that the gasis pumped out of said second chamber with well fluid, said valvecontrolled conduit means being operable to control the flow of gastherethrough as a function of the pressure level of gas being conductedtherethrough and the pressure levels within said gas trap and saidsecond chamber; means for injecting displacing fluid at a controlledrate into said first chamber, said means arranged for connection to asource of displacing fluid; means for expanding and contracting theeffective volume of said first chamber to displace up and down in saidchannel the region of interface between the displacing fluid and thewell fluid whereby the displacing fluid functions as a piston to pumpwell fluid in said inlet port means and out said discharge port means,said means being constructed for connection with a prime mover; andmeans for conducting fluid pumped from said outlet port means to wellsurface.
 15. The invention recited in claim 14, wherein said inlet portmeans includes a check valve operative to prevent fluid flowtherethrough out from said second chamber and said outlet port meansincludes a check valve operative to prevent fluid flow therethrough intosaid second chamber.
 16. The invention recited in claim 14, includingmeans for supplying displacing fluid, said displacing fluid supply meansbeing connected to said fluid injecting means to maintain the region ofinterface between the displacing fluid and the displaced fluid withinsaid channel and second chamber.
 17. The invention recited in claim 14,wherein said means for expanding and contracting the effective volume ofsaid first chaMber is a plunger means mounted therein for up and downreciprocal motion, said plunger means being adapted for connectionthrough a string of sucker rods to a prime mover.
 18. The inventionrecited in claim 14, including fluid injection means associated withsaid structure to extend into well fluid being pumped for injectingcontrolled quantities of a diluent fluid into the well fluid to bepumped whereby to dilute and thereby reduce the viscosity of the wellfluid.
 19. The invention recited in claim 14, wherein said means forexpanding and contracting the effective volume of said first chamber isa plunger means mounted therein for reciprocal motion.
 20. The inventionrecited in claim 19, including prime mover means connected to saidplunger means for driving said plunger means in its reciprocal path ofmotion.
 21. A well pumping system, comprising: a sucker rod string; afluid sealed string of tubing for positioning in a well to extend fromthe bottom portion of a well to well surface, said sucker rod stringbeing mounted in said string of tubing for reciprocation up and downtherein whereby said tubing functions as a housing to isolate saidsucker rod string from well fluid thereby up and down reciprocalmovement of said sucker rod string is not inhibited by well fluid; pumpstructure mounted on the lower end of said string of tubing to dependtherefrom into the reservoir of well fluid to be pumped, said pumpstructure defining a first fluid confining chamber in communication witha second fluid confining chamber through a fluid conducting passage,said first and second chambers being for holding, respectively, adisplacing fluid and a well fluid, said passage extending upwardly fromits point of communication with said second chamber to define anupwardly extending channel in which displacing fluid and well fluid mayinterface, said second chamber having inlet and outlet port meansoperable only to receive and discharge fluid, respectively, said pumpstructure having a gas trap defined therein above and in communicationwith the upper end of said channel to trap gas evolved from the wellfluid, and including valve controlled conduit means connected forconducting trapped gas from said gas trap to a point in said secondchamber adjacent said outlet port means so that the gas is pumped out ofsaid second chamber with well fluid, said valve controlled conduit meansbeing operable to control the flow of gas therethrough as a function ofthe pressure level of gas being conducted therethrough and the pressurelevels within said gas trap and said second chamber; plunger meansmounted for up and down reciprocal motion in said first chamber forexpanding and contracting the effective volume of said first chamber todisplace up and down in said channel the region of interface between thedisplacing fluid and the well fluid whereby the displacing fluidfunctions as a piston to pump well fluid in said inlet port means andout said outlet port means; means for isolating the discharge point ofsaid outlet port means of said pump structure from the well fluidreservoir and connecting said outlet port means in communication withwell surface so that well fluid discharged from said outlet port meansis pumped to well surface; means for connecting said plunger means tosaid sucker rod string whereby said plunger means may be driven throughsaid sucker rod string; displacing fluid supply means connected to saidfirst chamber for supplying displacing fluid thereto at a controllablerate to maintain the moving region of interface between the displacingfluid and the well fluid within said upwardly extending channel and saidsecond chamber; and prime mover means connected to said sucker rodstring for driving said sucker rod string in up and down reciprocalmotion thereby to drive said plunger means.
 22. The invention recited inclaim 21, wherein the well fluid is of an offensive nature and thedisplacing fluid is of an inoffensive nature.
 23. The invention definedin claim 21, including lubricating fluid within said fluid sealed stringof tubing to provide a lubricated path through which said sucker rodstring may reciprocate with minimum wear and substantially free fallvelocity.
 24. The invention recited in claim 21, wherein the well fluidis a high viscosity crude oil, the displacing fluid is kerosene, andincluding fluid injection means associated with said pump structure toextend into the crude oil being pumped for injecting controlledquantities of a diluent fluid into the high viscosity crude oil wherebyto dilute the crude oil and reduce its viscosity.
 25. The inventionrecited in claim 24, wherein the diluent fluid is kerosene.
 26. Theinvention defined in claim 21, wherein said means for isolating thedischarge point of said outlet port means from the well fluid reservoirand connecting said outlet port means in communication with well surfaceis a fluid sealed string of production tubing.
 27. The invention definedin claim 26, wherein said string of production tubing is detachablycoupled to said pump structure.
 28. The invention defined in claim 21,wherein said displacing fluid supply means is operable to supplydisplacing fluid to said pump structure in time coincidence with theexpansion of the effective volume of said first chamber.
 29. Theinvention defined in claim 28, wherein said displacing fluid supplymeans comprises: structure defining a reservoir for displacing fluid;means connected to said displacing fluid reservoir for transferringdisplacing fluid thereto at a controlled rate; and valve meansconnecting said displacing fluid reservoir in communication with saidfirst chamber for controlling the flow of displacing fluid between saiddisplacing fluid reservoir and said first chamber, said valve meansbeing operable to open and close, respectively, in time coincidence withthe expansion and contraction of the effective volume of said firstchamber.
 30. The invention defined in claim 29, wherein said valve meansis operated by the pressure differential developed between said firstchamber and said displacing fluid reservoir during the expansion andcontraction of the effective volume of said first chamber.
 31. Theinvention defined in claim 30, wherein: said displacing fluid reservoiris defined by a downwardly extending continuation of said first chamber,said displacing fluid reservoir being in alignment with said plungermeans; and said plunger means seals said first chamber from saiddisplacing fluid reservoir whereby the up and down reciprocal movementof said plunger means to contract and expand the effective volume ofsaid first chamber, respectively, expands and contracts the volume ofsaid reservoir means; and said valve means is carried by said plungermeans.